xfs: move all writeback buffer_head manipulation into xfs_map_at_offset

This keeps it in a single place so it can be made otional more easily.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_aops.c

@@ -494,21 +494,6 @@ xfs_map_blocks(
 	return 0;
 }
 
-STATIC void
-xfs_start_buffer_writeback(
-	struct buffer_head	*bh)
-{
-	ASSERT(buffer_mapped(bh));
-	ASSERT(buffer_locked(bh));
-	ASSERT(!buffer_delay(bh));
-	ASSERT(!buffer_unwritten(bh));
-
-	bh->b_end_io = NULL;
-	set_buffer_async_write(bh);
-	set_buffer_uptodate(bh);
-	clear_buffer_dirty(bh);
-}
-
 STATIC void
 xfs_start_page_writeback(
 	struct page		*page,
@@ -728,6 +713,7 @@ xfs_map_at_offset(
 	ASSERT(imap->br_startblock != HOLESTARTBLOCK);
 	ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
 
+	lock_buffer(bh);
 	xfs_map_buffer(inode, bh, imap, offset);
 	set_buffer_mapped(bh);
 	clear_buffer_delay(bh);
@@ -740,6 +726,10 @@ xfs_map_at_offset(
 	 * set the bdev now.
 	 */
 	bh->b_bdev = xfs_find_bdev_for_inode(inode);
+	bh->b_end_io = NULL;
+	set_buffer_async_write(bh);
+	set_buffer_uptodate(bh);
+	clear_buffer_dirty(bh);
 }
 
 STATIC void
@@ -861,11 +851,9 @@ xfs_writepage_map(
 		if (wpc->io_type == XFS_IO_HOLE)
 			continue;
 
-		lock_buffer(bh);
 		xfs_map_at_offset(inode, bh, &wpc->imap, file_offset);
 		xfs_add_to_ioend(inode, file_offset, page, wpc, wbc,
 				&submit_list);
-		xfs_start_buffer_writeback(bh);
 		count++;
 	}